Metallurgical furnace



C. E. THOMAS ETAL METALLURGICAL FURNACE Bec. M, 1948.

Filed June 1o, 194s 4 Sheets-Sheet 1 4INVENTORS C. E.THOMAS J. S.FE'LTER BY nog ZI DSC. 14, 1948. Q EI THOMAS ETAL 2,456,469

K METALLURGICAL FURNACE 4 Filed June l0, 1943 I i 4 Sheets-Sheet 2lNVENTORS CE THOMAS J. S. F ELTER H.J.NEss Y 'A R Y C. E. THOMASE'I'AL.-

Dec. 14, 1948.

METALLURGICAL FURNACE 4 Sheets-Sheet 3 Filed June 10, 1943 INVENToRs yC.E.THOMAS J. S. FELTER H.J. NESS Dec. 14, 1948. c. E. THOMAS ETAL YMETALLURGICAI.:y FIURNACE 4 Sheets-Sheet 4 Filed June 10, 1943 INVENTORSC E. THOMAS J. SFELTER BY H. J. N ESS TTRNEY will be prevented.

burizing, depending upon the nature ofthe carrier gas. In order toprevent the muflie atmosphere may be either neutral to the work orcarphere from being driven from the mufiie when the cover is removed,suitable control means is,-

arranged to be operated by removal of the cover to interrupt theoperation of the circulating means and by replacement of the cover torestart the operation thereof. l

Numerous other features of the invention will be apparent as thedescription proceeds. i-'As will be evident from the foregoing, one ofthe principal objects of the inventionV is to provide a furnacenf thetype described, in which there fwill be no' load upon the muiiie or uponAthe refractory furnace walls, thereby permitting -the muille to be madeof thin walled alloy and the furnace walls to be made of light, porousbrick of highinsulating value.

Anotherobject is to prevent 'damage to the -rnullle orv-to thefurnacewalls due to frequent 'removal ofthe cover and the charge from thefurnacel` and the replacement of the cover and insertion of anew chargewithin the muille.

FAnother object-of the invention is to support the work to be heatedindependently of its conif' taining mullie or of the refractory furnacewalls. Another object is Ato facilitate the loading and unloading of thefurnace so that these operations may beconducted quickly andconveniently and with a minimum-of heat loss from the furnace. "Stillanother object is to support the work parts inl the rfurnace out ofcontact with the walls thereof and with each other whereby there will#be no local-hot or cold spots on the work and 'whereby the furnaceatmosphere will have free f access to all parts of the work.

Anotherobject is to preclude the presence of -pock'etsof trappedair inthe work parts, carried into the furnace thereby,

parts, will vbe rendered nonoxidizing to the parts `byl chemicallreaction with the furnace yatmosphere. i .f

Another object is to provide `a progressively advancingA oxygen'rlxationfront from the inlet of the protective atmosphere to the muille outlet,

'Still 'another object is to provide a furnace inl y' Vwhich-ahy airentering into the furnace during loading or carried into `the furnace bythe work following the introduction of a load of work parts into thenuille. 1

f `Another object is to provide a muiile furnace of the pit type heatedby an external combustion chamber in which leakage of r`the products ofcombustion from said chamber 'into the muiile Another object of theinvention `is to provide a suitable,V seal containing displaceablematerial `material duringthe sealing support for the removable coverandfor the work parts.

A still furtherfobject is to provide an even and A uniformheating of themuille. l

Still another object is to provide a novel ar- Sentence Fig. 1 is avertical sectional view of a pit type furnaceembodying a number offeatures of the present invention, taken on the line I-I of Fig. 3;

Fig. 2 is a plan view of the furnace showing the removable coverthereof; f Fig. 3 is a sectional view on the line 3 3 of Fig. l, showingthe arrangement of the burners for the combustion chamber and theatmosphere inlet for the muiile;

Fig. 4 is a sectional view on the line 4'-'4-of Fig. 3, showing thelithium generator employed therewith for conditioning the furnaceatmosphere;

Fig. 5 is a sectional view on the line 5-'5 o Fig. 1, showing the workparts and work retaining ring;

Fig. 6 is an elevational view of the furnace, showing the arrangement ofthe burners and the manifolding thereof;

Fig. '7 is a developed view of the furnace shell on a reduced scale,showing the arrangement of the burners; y

Fig. 8 is a layout view, showing the arrangement of a number of furnacesof the type shown zin Fig. l in connection with a common carrier gasrnumber of columns I5. A reinforcing ring I6 is welded about the openupper end of the shell lI0, and an annular angle I1 is welded to theshell at the floor level to serve as a support for the grating I8forming a cover for the pit I3.

The shell I0 is lined with refractory brickwork composed of a base I9 ofhard burned brick and a side wall 2I of alight, porous brick of high in-.sulating value. A cylindrical muille 22 is disposed v.centrally withinthe brickwork, resting directly upon the hard burned brick base I9 andspaced from the side wall 2I to form a combustion cham- -ber 23, and theside wall ZI is corbelled at 24 t0 `Ineetthe muiile 22, to form a rooffor the combustion chamber. extending tangentially through the side wall2l ,are arranged on an ascending helical line of in- ,creasing pitch,Fig. 6, whereby the greatest con- ,centration of burners occurs near thebase of the lcombustion chamber with a progressively greater A number ofburners 25y Fig. 3,

spacing vbetween the burnersV upwardly, thus compensating for theincreased heat at the top of the 'muiiie due to the tendency of theheated gases to rise in the combustion chamber, and thus maintaining themufe 22 at a substantially uniform temperature throughout its length.The circumferential spacing of the burners is such that the burnerslocated on one turn of the helical line are 5 .positioned'crculniereritial'ly i'intermlediate ithose on adjacent iturns. @neLarrangemerit of fthe burners --is kshown in the developed viewof theshell "Folin Fig. 7,'infwhichburnersfare indicated -byithelettersa'tomThe'spacing between burners 'of-each turn `is -such that there willbefanodd xnuniber o'fburners ineach t-woiturns dfthe helix. This4arrangement fenellil-es maximum spacing tbetween 'the eigmrners ofadjacent turns 4to "be obltained, 1which promotes better bon'ding fI'the lwall 'and reduces the danger of weakwertical izon'es therein,particularly fadjlacent the "base VWhere ithe sp'iral is relatively'flatand l the=vertical spacing between burners 1is small. 'It Lalso prometesIamore continuous spiraling Jand swirling `recess?? -formedlintheshell'li). The burner-"exif ten'cis *through the 'Wall 'of fth'e recess2l, and throug'ha hard-"burned 'brick 28, terminating -irr a 'moldedrefractory burner bloc-k A29 which 'forms'anfoutwardlyilaringburnertunnelSD connecting 'with a passage 3'! intherefractory side wall.

'The "angle of'the'burner and theburner tunnel is suchthat its laxisissubstantiallytangent Itov the 'froid-'circumference fof 4the 'combustionchamber, `thereby p'emn'itting the combustion gases toA swirl'aroundthecombustion chamber wit'haminimum ofinter'ference from thewalls 'of the 'combustion chamber 4and with anaturalow into the gasstream issuing from Cthe rnext adjacent burner. The movement of "theAgases is thus laugmented V'by *the gases issuing from each suceedingburner,` producing a smooth spiral Liiovv oi considerable *velocity'around vthe outer VAwall Aof the muffle 22. -*Due to Ycentrifugalaction,`the gases scrub the Y"innerwall o'f the J'brickworlg Whichf'aidsin'lthe extraction ofthe neatfromv'the gases and'a uniform fh'eating'd-fthemuiile by' radiation from the h'otbrickwok "Fheburners `25'areprovided'with a combusti- 'ble mixtureof V4air and gas lfrom a 'pair ofKmani- Tolds `32U^a;nd"?'2L (Figs, '1, y2, 3, and ii) "disposedabout`sthe-shell I'Uand supportedthereontby suit- 'ablefbracketsTheupper m-ariifoldiSZU servestlre iburnersiintheupper 'halfv of thefurnacegand the manifold '32L serves Ivthe lower group of burners. 'Each'manifold vis provided with "an electricallyr "operated supply .valveSSUand SSL, whichscontrolled "by 'an individual 'pyrometer '34U and 35L, k*located `in the "zone serviced by jthe respective `manifoldthrough vadjustable galvanometer switches '3 5U, 351'.. and `mercuryswitches "SBU, 3'BL. "Thus, 'the upper'and lower zones `of 'the 'furnaceare separately controlled to aid in 4maintaining :a uniform temperature"throughouttheflength .,of the"mu"ie. The vproducts 'ofcombustion areexhautsedfrom'the chamber 23 by'twosets 'of exhaustgports STU 'and 31L,the former :consisting 'of three ports located just below fthe` upperjgroup "of burners Aandthe latter, asbest shown in'Fig.3, 'consisting ofthree ports located just below 'the ,'lowerset'ofburn'ers."Each'exhaust, port-isformed fof aheat'resisting alloy tube extendingthrough thebric'kwork and serving to conduct thegases *toia Asuitablestack Aor ventilator, not. shown. '.The mrovision "of .a `separate set'of exhaust ,ports for 'eachof'thesets'of burners also'aidsin maintainixlingamidiforrmternpenaturent/ithintheiuflielsinele =the two fsets of rburners 'will operate fon indifferent 61T andon`timie'intervalsluniiertheirimdis -vdual controls.

The opentupperfend'ofithexmuiileicisnlcsedby a :removable cover 39comprised cof I. a imetal shell 4containing rrefractory 1heat insulation'M -shell formed by two spaced discs ortplates m2 and 43 Iseparated ibyff-an r annular ringffornre'd'frfa VVchannelfmeniloer M, 'an-angle'1515,:a'nd-g tlibe for pimms, eacnweluedito'lits adjoiningfmemeer. :neannular ang`1e^f41 welded to 'the pipe 24-6 #forms a -Seat for theilower plate 43, ywhich .is of iheat :resisting/alloy. A numberofigussetfplatesidiane `Weldedbetween Lthe pipe Alili andi-the angleito`reinforce =the same r'and 'to .absorb lanyrshock'iim# partedl'thereto'by thefcover centeringi meansdur- -`ing thelowering ofthecover toits seat. iThis eenfteringmeans Willbe described subsequently.'The `'toveriis reinforced by fourlsubstantially diagonal AIibe'ams '-48subtended by `'four Ibeams 51. jshort `-section of -rI-beam 52 extendsbetween the intersections of the I-beams 149. A-ll'ofthesemeinforcingbeams are weldedto eachother and to the channel-meinteer-l'liv and arer4forthe purpose'o'f jprovi'ding a' strong, rigid structurefromwhic-hithe lheavy work parts lto b e Itreatedmay'bel-suspendedWithinthe'muie, as willhereinafterfappear.

"The cover .39 lWith `"the n/'orkfparts 4to be ssuspen'd'ed therefrom is"supported lindepen'clentlyfdf 'the mu'ile .22 and the brick side Wall2`gl uat a part o'f 'the Y'furnace which is maintained Vat -f'aArelatively A'lovv "temperature, For this purpose an annular angle ".53is Welded to the interior ofthe shell with its upper -face 'slightly'above :the 'top of the "brick sidewall 2i andthe'miilie 22, thereby.maintaining '3a space 'between *the'bot- 'tom cover plate *43 .andthese members -vvvhen ithe cover 'is .resting upon "its 'seat 53. Thus,`neither the 4cover "39 wnor lthe Work parts can "imposeany loadontheAmulileorron itsesurroun'd- 'ingbri'ckwork or'eiectany'damage thereto.A'a "consequence,v l thernu'ilie 22 may '-havefa rela- `tivelstliinWall, su'fcient only'to Supportitsown Weight'tvhenheated- T'lhisresultsin alargefsavfing of anetal antifa substantial-economyinconstructioncost. It also promotesmore Arapid heat 4transferfromrthe'combustion gases in the-'outer fchaniber'23. e

In `order to 'seal theinterior nf the muliie ""22 from *the 'combustionchamber Q3, 'an annular "trough ".54 iis Aformed 'at `the Aupper "end ofthe muflie in which a suitable displaceable sealing material "55 'may becontained. Preferably `this materia-l is `granular :chromeioresubstantially free 'of powder and 'of a suflicient .size to 'have a`loWangle of repose,.so astopreven't packing and to "permit -l'eatlydisplacement 'therecif, Vailvlthough beach sand Aor other suitable'refractory ,sealing material ,may Lbe use'd. An annular orring 56,depending from the coverplate 313, "is'providedfor .entry into thetrough "54 to com lplete @the seal. This .ing56` is"beveledat itslower'edge to facilitate yd isplacement ofthe sealing .materiaL f A similarseal, comprising ,an annular trough '5l Aformed in the brick side Wall"2l, a sealing medium 58, and a cooperating dependinggsealing ring 59,provide aheat ,seal lto'isolate.-tllercover .supporting ring 5'3 from'the combustion gases. VThe depending 'length of thesealing rings .55and 59 is such that they 4engage in ,the troughs "54 andl5l only afterthe cover 31lhas progressed into the feXtended :upper `end Aof thefshellgill a short distance, thus insuring correct centering 7 ofthe .coverover the inuiil'e and proper alignment ofthe l'sea-ling rings over theirrespective troughs beforey entry of the rings intoithe troughs.` Pcs'-sible damage to the sealing rings, or to the Inutile, or the .brickwork,by accidental engagement f the sealing rings therewith is thusprevented. Inorder that there will be no sudden shock irrifparted to themuiiie 22 by the sealing ring 56, transmitted through the sealingmaterial 55, lshould the cover be lowered to its seat atan abnormalrate, the 'outer sealing ring 59 is made of considerably greater wallthickness than the ring 56 which, together with its greater diameter,gives it a much larger area of contact with the sealing material thanhas the inner ring 56. The 'shock of a sudden movement of the cover toits seat will, therefore, be taken up primarily by the outer ring. Tostiifen the upper end of the muiile 22 and protect it from` accidentalknocks, as from the work parts, if improperly loaded, and to retain thesealing medium therein, a beading 6| is formed about the upper end ofeach .wall of the trough 54.

3 The parts to be treated are shown in4 Fig. 1 as comprising tubularblanks 62 for use in the production of steel propeller blades foraircraft. 'Ihese lblanks are threaded at their upper ends for subsequentattachment to the propeller hub `and these threads are utilized tosuspend the blanks within the muille 22. y For this purpose a`hollowplug 63, having apertures 64 therein and a hook 65formed-thereon, is threaded into the blanks. The apertures 64 areprovided for the lescape of the air contained within the tubes .whenfirst loaded into the furnace and for cr- .culation of the protectivefurnace atmosphere wtlflerethrougl'i during the heat treatment, as willhereinafter appear. The blanks 62 are suspended from a plate 66 havingstiffening ribs l61 cast thereon and provided with a group of Mdependinghooks 68 secured theretoy as by means ofnuts 69, for interengagement'with the hooks `65. The plate 66 extends to adjacent the side wall ofthe muiiie 22 and its lower surface is conca-ve so that it will serve asa baffle to direct the muiile atmosphere in a circulatory path, as willhereinafter appear. It is carried by the .cover 39 through a quicklydetachable universal coupling comprising a double shackle, member 10having its pins 1I and 12 disposed at right angles. The shackle issecured by its upper pin 1I to a rod 13 Xed to the cover I-beam Section52, as by bolts 14, and the baille plate 66 is susjp'ended therefrom bya rod 15 passing loosely through the plate 66 and having a nut 16 on itslower end. The shacklelpin 12 is removable and passes through the eyesof the shackle and rod 15. In order to limit swinging of the plate 66 onthe shackle bolts, a number of upstanding posts or lugs 11 are providedon' the plate 66 extending to adjacent the `cover 39. Swinging of theblanks 62 on the hooks 68 is prevented by concentric retaining rings 18and 19, Fig. 5, removably carried by a depending rod l8|] vrigidlysecured to the under side of the plate 66. The ring structure isspidered to a sleeved hub 8l having a pin and bayonet connection to asleeve B2 carried by the rod 8D. Thus, after the blanks 62 have beensecured to the plate 66 externally of the furnace, the retaining ringstructure is slipped up over the ends of the tubes and fastened in placeby the sleeve 82.

A protective atmosphere is introduced into the muiile 22 under slightpressure through a conduit 83 and is exhausted therefrom by a vent 84extending through the cover 39. The' ess caping gases are ignited by apilot burner 85 carried by a pipe 86 extending over the cover 39.Y The'pipe 66 is threaded in the elbow of a swivel coupling 81 bolted througha squared iiange '89. to a bracket@ carried by the furnace shell. Thecoupling 81 communicates with a gas supply conduit 9B, Fig. 2, having asuitable valve 9| for regulating the length of the ,pilot name. Theburner 85 is adapted to be moved away from the cover 39 and back intoposition to re-ignite the vented gas, upon the removal and displacementof the cover, by a lever 92 pivoted on the sleeve section 93 of thecoupling and clamped at 94 to the pipe 86. The outwardly extending endof the lever 92 is pivotally connected by a link 95 to the plunger rod96 of a piston 91 contained within the cylinder 9815ecured to thebracket 88 by the lugs 99. Air under pressure is admitted alternatelyabove and below the piston 91 by a reversing valve 100 operated by asolenoid |01 controlled by a switch |92 in accordance with the positionof the cover 39. A switch operating lever |03 pivoted on the bracket 88has one end extending through the shell I0 into the path of the cover 39so that with the cover in closed position the lever will be depressedand its outwardly extending arm will be held out of engagement with thecontact arm 104. Therefore, contacts [92 will remain open and contacts|05 will be closed. In this condition of the switch, solenoid 16| willbe deenergized, and the reversing valve IUD will be s o positioned as toadmit air to the under side of the piston 91 whereby to retain thepiston in its uppermost position so that the pilot burner 85 will belocated over the cover 39 of the fur;- nace in position to keep theexhaust gases from the furnace ignited. However, upon the initialmovementfof the cover upwardly, lever 103 will rock under action of thespring 106 to close contacts |02, and energize the solenoid HHV so as toreverse the valve l. Air pressure will then be applied above the piston91 to draw the ylink 9 5 downward, and thus rock the lever 92 and pipe86 to the vertical dotted line position away from the cover 39. Onreturn of the cover 39 to its seat, the reverse action occurs, and thepilot burner is returned to its horizontal position over the furnace toreignite the gases escaping from the vent 84. Since the vent 84 isdisposed substantially centrally of the cover, the pilot flame willignite the escaping gases irrespective of the angular position of thecover on its seat; thereby no indexing of the cover is required. Withl acommercial size furnace, the pipe 86 will be sufliciently long toelevate the burner above the iioor at such height as to produce nohazard. It will .be understood that the pilot burner will be pivoted atthe side of the shell l0 remote from ,the direction of loading andlunloading of the muiile.

The loading and unloading of the furnace is effected by a travelingcrane or hoist having a chain gear which engages the cover 39 by meansof four eyes 108 suitably anchored to the lower flange of the channelframe member 44. The operation of unloading the furnace comprises thelifting of the cover and its load of Work parts vertically so that thework parts clear the top of the furnace and a lateral movement of thecover to a point where the work parts may be lowered between a pair ofsuspendedrails upon which the plate 66 may rest. With the load thusremoved from-the cover 39, the shackle pin ."12

9? may: be." removed:4 the cover, positioned. over another.t plate 6&6#carrying. an cold load; I'heY shackle` pin:` is:` reinseifted and: thecover andi cold; load... conveyed a pointl. vefticallyf above' the:muffle- 22? and then: lowered in pla-ce.y In order: to..l center thecoveru in: thefsh'ell. 0i and; align ther sealing.. rings 56 and: 591with: their troughs;-, a number: ciz centering guides lilili are.secured: to\ the'fupperzedge` of the turnacefshell... Eachbf.- theguides lSr comprises# a U-shaned. brackets. the upper" edges of-r whichslopeA outwardly. from the: cover, and .aiseriesz oflneedle :rollers |P|loosely.- journaled in. grooves; |=|-|.r im the: opposite: arms ofitheebracket.. The brackets aref securedy to. thefshell in any suitablemanner, as by We1ding;. In@ lowering' the` cover. into position; shouldit be slightly? oft center', ,thefafnnulan pipefdz; Awhiehzhas:-a-.relatively-1ar-ge radius, will: engagesl onefor-theother.offthefguidestolgive-it the. required laterali movement.- tocenter itwithI respect-Lto? the munie.- L

and enable it. to pass' freely intox ther furnacef opening..v

To. promote.L the circulation off the atmosphere? through* and aroundthe blanks; er fan: |.|2f' is.

provided; inthe; base of. the` muflle-,. driven. from u asuitablev motor|f| 3. by,r meansoir a. belt. Movandl ashaft M5.. The. shaft. ||15extendsi through. a" tubular. extensionr of the. muiilef 2lM and is:provided with a... pressed: graphitel bearing; lli!A within. the tube:andrwitha pair. ci ball,P or.V

roller bearings.. |.|8, carriedbya. bracket irl-hse tube H1B" is sealedby a.. gland |2ll' and:l is. pro vided'- with anumben otheatAinsulating. disks |'2.ll: fn baiting; theJ iiow.v ofi. hot tube |16.'andfoi; conducting; the heat. away.y from the shaftISand'theglandfl-Zilr Ii desired the; gland;v may. be cooled by eitheran air streamer' by ci'rculatihr; water. thereabout, asby thecoil. |22.E tubular fan.. housing |231 elevatedlfrom, the iloor of the. muiileAonlegsf or. brackets sur rounds theV fan. |.'|'2 andlt'ends to. direct.the.at.- mospliere stream upwardly through=and around.' the work partsG22. It.. is. coveredl witlrafwirefl mesh. |211 to diffuse the. gases.andr guettent-injury tof the' i'an. by any.A Work. parts. or.. other.objects.` dropped'int'o' the muilie accidentally.

The` atmosphere. forcedf. upwardly by the fans through the center. ofthe muiil. into and'arcund the iubes' 62 is. deflected at. the. topoffthe. muilie; by the baille plate 5B). passing, towards thesidey Wallfof the mufe and.` sweeping, dow-never the. heated* surface thereof' in.a. verticali circulatory path; A portion ofthe atmosphereipasses around.the edge of" theplate:6b"and` escapes thlloughithe vent 8`4, Where itisignitedl. 'I'lieburriingdv gases. at the vent 84. serve' as. an.indication ot the.' conditionV of themul'e atmosphere, burning. with.the`A characteristic' scarlet col'or of" lithium when the atmosphere? isproperly conditioned. The opening throughthe vent 84 is of such, size asto` maintainaslight*k pressureI Within' the munie.

The operationz off' thefarr |12" is` controlled b'y t'li'ev removal andreplacement or the cover S'SI through the switch contacts |05operated'by the switch. lever |413. Withi ther comer in. position, thecontactsA |05 will.. be closed. and` the motor circuit completed,but'upon removalof the cover these contacts: will be` opened tolquickly# inter'- rupt. the: motor.' circuit-L and stopthe fan sothatvlthefhotsatmosphere inftliefmuilly will. not. be driveniunaboutnthosides crit-he cover asitl. is lifted'zfrorrrl its.: seat.'llieffan then remainssoutf ofV operationrthrouallcutthe'entirefumloadingfandmeloading onerationi.

gases through the :l

the operation of 'Ilhe inlet conduit; 83. for the.- muflle Latmosiphere.

encircles ther` fan housing. |23.A below' tholower. edge thereo Ity isprovided,I with. atseries of. slotsr 25.` on its inner face fortheadmission of,

j. the protective gas into the Inutile;.radial-1y in the.

directionof circulation... ofthe muiile atmosphere as producedv by theAfany M2 when. it. is) in ope-r,-v ation. In addition.I toproViding.aruniformldisf.

tribution: ofthe. lithiatedl gas to. ther blower, thel extension.-ofthe` conduit 83 throughthecombusw tion chamber 2r3sand.infa long.path. inithe` base. of the muiile. enables. the incoming. gas.. to.l be.brought-K upto the. muilleV temperature' before. issuing into the.muflle; Thispreheatingof'tle;

-lithiatedgases. promotes the reaction.- of the the muflie 22,andasubstantiallvolume ona-inis also carried intoith-e mule within thetubular wor-k. parts. Toexpedite thefremovaLof, the fromthe muiiie,andior.. the. 'xationoi. theoxygen contained` therein, by. theprotective. atmosphere introduced.v into'thebase .ot the. muliie, ,itis.preterable :to retain. the. blower. atrestior. ashort afterthefcover-hasbeen replaced.. Eor.this..pur pose theswitchontacts. |05',vwhichiareclosedby. the. replacement, of. thacoyer, ,do not immediately.energize the motor, a delay being intrtoducect'by.` a time delay. switch|2, such..as an .electrie timer or a dashpot relay, .thus holding the.blower. cirouit. open. for. aA sufficient period.. to substantially.ri'd. the.A mufle. of` the. air or. oxygen .thereirn The. time. delayswitch.. |251 may be adjusted son that; its. contacts.. will. not. closeuntil.. after. the tell,- tale scarletame.. appears at the vent. 84'..

The restoration. of; the. desired. protective. at.- mosphere inthemuleis.notdependentuponthe physical displacement. of theair byrhein-coming gas, but primarily. upon achemical fixation ofLthe oxygenandwater Vapor. content, thellattereffeetl beingV obtainedl from thelithium introduced therein. Lithiumhasa strongaaffinity. for oxygen andUpermeates the munie chamber, penetratingv into the interior of" th'etubes (i2and.chemicallyv uniting with any oxyeenor` water vapor. thereinto x the same, as will. presently appear- As. stated-when the col/er 39.of the. furnaceis removed, the lithiated` atmosphere. in. the.. muiileescapes and is replacedby air. The ian. |'|2.`is.at rest at4 this time,and! the. lithiated. gases issuing; from the, apertures` 2F the.conduit, 33T into. Contact with this air burn in the base oiltheInutile. When the cover. 39S is rst replacedthe.

fan is. still`retained`, at rest, .but asthe OXygerLad.- jacent theapertures l25iscon'sumed. the incom.n ing.lithiatedgaseswhich' are onlypartially. com.- bustedg' spread' out' radially 'and upwardlyfrom theconduit' 83,' forming a. substantially. continu.; ous'at'mosphere front'which'..progressesuprvardly., displacing a partv of the air. through.the,v vent 84 and consumingthe oxygen in. contact. therewith as. itadvances upwardly. The oX-ygenisinpart. converted'by the CO andHz oftheincomingg'ases to CO2l and H20; and these together with. any.remaining oxygenare xedby. the lithium. of the. carrier gas; Byretaining` the4 fan 2 at.` rest, during thisV cleaning' up period, thiscombined. flame propagation' and' oxygen xation iront...is

11 permitted to advance upwardly of the mule without intermixing of theair and the carrier gas, with a progressive fixation of the oxygen andwater Vapor content of the air as this oxygen xation front advances.

When the lithiated gases reach the top of the muiiie and start escapingfrom the Vent 84, they will be ignited byv the pilot burner 85, and thisflame will gradually assume a rich scarlet color, indicating that themuille has been entirely freed of any unxed oxygen. When this scarletflame appears, the fan ||2 may be started, and the dashpot relay |26 maybe adjusted to provide a time delay sufficient for this purpose.

In order that the furnace attendant will know when the fan ||2 isoperating, a signal lamp |21 is provided mounted at any suitableposition, either on the furnace or on the control panel, operated inparallel with the fan motor I I3.v

Y The inlet pipe 23 for the muiile atmosphere extends from a lithiumgenerator |28 suitably secured to the outer Wall of the furnace, as bylugs |29, As shown in Fig. 4, this generator comprises a metal chamber|3| having aremovable cover |32 from which a plate |33 depends. Aroundthe chamber |3| is disposed an electrical heating coil |34 containedwithin suitable refractory insulation, and within the chamber there is acentral cylindrical recess' |35, in which is supported a metallic cup|36 containing suitable lithium compounds. A carrier gas is admittedinto the lithium generator through a conduit |37, this carrier gas`being deflected by the partition plate |33 over the cup |36 and thenceby way of the conduit 83 into the muffle 22.

The carrier gas may be a non-oxidizing me-- dium, such as nitrogen orhydrogen, although a gas resulting from the combustion or cracking of aliquid or gaseous fuel is preferred. Air may also be employed as acarrier gas, if desired= since the lithium fixes the oxygen therein.However, the use of air as a carrier gas requires the consumption of agreater quantity of lithium and is not preferred; Fig. 8 shows apparatusfor producing a suitable carrier gas bythe combustion of an air and gasfuel. Hydrocarbon gas, such as butane, propane, or natural gas, suppliedfrom 'a conduit |38, and air drawn in through a conduit |39, eachprovided with an apertured plate or disc |,4I for metering theproportion of each, are forced under slight pressure by la pump orblower |42 into a closed cracking chamber |43. The chamber |43 is heatedby a series of burners |44 extending tangentially into the combustionchamber |45 of a furnace |46 in which the chamber |43 is contained. Theratio of the hydrocarbon gas to air is dependent upon the analysis ofthe former, and the purpose for which the muile chamber is to be used.For the heat treating of metals, where a neutral atmospher-e is desired,We prefer to employ a ratio of approximately l part of propane to 18parts of air, whereas for carburizing a ratio of 1 part of propane tofrom 4 to 12 parts of air may be used, depending upon the analysis ofthe gas and the type, analysis n and quality of the carburized casedesired.

The furnace |46 may be of similar construction to the furnace of Fig, l,with the closed cracking chamber |43 substituted for the muflle 22. Theburners |44 are supplied with fuel and air from an independent source toprovide heat of approximately l800 to 1900 F. for cracking of the gasesin the chamber |43, as fully described in Patent No. 2,346,698 of H. J.Ness, granted April 8, 1944, and entitled CQntlOllQd 12 atmospherefurnace. Thecracked gases from the chamber |43 are passed through acondenser |41 where they are cooled and the major portion of the wateris removed. A condenser suitablel for this purpose is shown in thePatent No. 2,394,002 .of H. J. Ness,` previously referred to. The cooledand partially dried gases'are conducted by a conduit |48 to a manifold|49 from which it is distributed to the lithium vaporizing chambers |28of a number of treating furnaces A, B and C, similar to the furnace ofFig. 1 As stated, this gas in passing through the chamber 3| picks upthe vapor emanating from the lithium compound in the cup |36 and carriesit into the muiile 22.

The preferred charge within the cup |36 comprises a mixture of lithiumcarbonate and lithium chloride in the proportion of about 60% of theformer and 40% of the later, by weight, which has been fused together ata temperature of about 1800" F. With a fused mixture of theseproportions, sufficient vaporization occurs ata temperature of aboutl300 F. to create an appreciable lithiated muille atmosphere, althoughhigher temperatures may be employed depending on the amount of lithiumdesired in the atmosphere. The amount of lithium salt required toproduce a non-oxidizing and non-decarburizing and nonstaining atmospherein the muiile 22 is very small. With a muilie heated to 1400 F. andhaving a volume of approximatelylO() cubic feet and provided with amixture of air and gas entering the gas generator at the rate of about1200 cubic feet per hour, a 7 to 8 ounce charge of lithium saltscomposed of 40% lithium chloride and 60% lithium carbonate, heated inthe vaporizer toa temperature of 1800 F., will supply sumcient lithiumto the atmosphere within the muille to maintain'the same for a period of12 hours or more in a condition which is neutral to steels or othermetals so that neither oxidation, nor decarburization, nor staininingthereof will occur. While it is desirable to maintain the charge in theVaporizing chamber |3| at a temperature of at least l800 F. for the saltmixture specified, the

muille 22 may be operated at temperatures ranging from 450 F. up to themaximum temperature that the muffle will withstand.

While the exact nature of the chemical reactions occurring in the chargein the cup |36 or between the generated vapors and the combustion.

gases from the cracking chamber |43 is not fully known, the followingexplanation is supported by a large amount of experimental evidence.

The lithium chloride within the cup at the temperature prevailingtherein is reduced to lithium metal by reaction with thehydrogen of thecarrier gas in accordance with Ythe equation The hydrochloric acid soformed then reacts with the lithium carbonate or any lithium oxide inthe cup to produce additional lithium chloride as follows:

2HC1 LizCOs 2LC1 -1- H2O -1- CO2 2HC1 -l- LizO 2LiC1 -i- H2O The lithiumchloride formed by the above con'- version reacts with hydrogen, as setforth above, to liberate a vapor of lithium metal. i

. In this manner the lithium carbonate is gradually converted to thechloride and thus to the metal, as the process proceds. The proportionof 40% lithium chloride and 60 %v lithium carbonate appears to be sobalanced as to render the hence, a sharply peaked secondary voltage,.the eifect of which is accented by a tuning condenser |16 across thesecondary winding.' The rapid vibrations of the armature |13 arecommunicated through the rod |69 to the plate |'65,'and thence to thesealing ring 56' and to the sealing material 55 adjacent thereto,causing the latter to become fluid and enabling the sealing ring toreadily penetrate the same as the cover islowered to its seat. A switch|11 in the vibrator circuit permits the vibrator to be operated onlyduring the cover opening and closing operations. The switch |11 isnormally open but is arranged to bel operated by a slide |18 extendingthrough a slideway in a block carried by the furnace shell Il! into thepath of the ringA |19 which encircles the outer end` of the' I-beam's|59. Consequently as the rings 56' and 59 approach the sealing medium intheir associated troughs, the slide |18 is engaged by the ring |19 andcammed outwardly thereby to close the vibrator vircuit. This circuitremains closed until the sealing rings are substantally fully engaged inthe sealing medium and the cover fully seated upon the support |62whereupon the' slide is released to open the vibrator circuit;

In Figs. 9 and 210 a modified form of work holder and baille plate 61'is shown, comprising ay disc |80 having a series of radial ribs |8|thereon extending outwardly from the hub |82 to a series of workholdingcups |83. Slots |`84 extend inwardly from the periphery of the disc intothe cups. The blank holders |85 each comprise anr apertured plug |86threaded' to the blanks 62 and having a shank |81 terminating in a ball|88 adapted to lt Within the cups |83 when the shank |81 is passedthrough the slots |84, thus providing a universal connection with theholding disc |8|lV and permitting the tubes 62 to hang verticallyirrespective of the langular` position of the disc. i

` The disc |80 rests on an enlarged portion |89 of the stud I9! by whichit is carried from the shackle 10 by the removable pin 12. The lower endof the stud |S| has a cylindrical recess |92 therein adapted to receivea vertical stanchion orpost, not shown, to support the disc and its loadof work parts when it is removed from the furnace for cooling. Thefurnace of Fig. 9 is otherwise similar to that shown inFigs. l to 4.

`Itwill be understood, of course, that many modifications andalterations of the structure shown'and described may be `made withoutdeparting from the essential attributes of the invention, and all suchchanges are contemplated a-s coming within the scopel of the appendedclaims.

What is claimed is:

. l. A furnace comprising a vertical heat treatl ing chamber having anopen top, heating'means for said chamber, a removable closure member forsaid chamber, means for supporting said closure member on said furnacestructure independent of said heat treating chamber and a plurality ofconcentric gas seals between said heat treating chamber and saidsupporting means, one of said seals being disposed between said heatingmeans and said supporting means and another of said seals being disposedbetween said heat treating chamber' and said heating means.

2. A furnace comprising a heating chamber, a muflle disposed in saidheating chamber and hav- -ing an open top, a closure member forsaid'mufile, means vcarried by said closure member for forming a gasseal between said heating chamber and said mufe, a support for saidclosure member disposed rem'ote from the heating chamber and a heatsealv between said heating chamber and said support adapted to be closedby said closure member.

3. A furnace comprising a heating chamber, a muiiie disposed in saidheating chamber and having an open top, a closure member for saidmuiiie, means carried by said closure member for forming a gas sealbetween said heating chamber and said muie, a support for said closuremember disposed remote from the heating chamber, a heat seal betweensaid heating chamber and said support adapted to be closed by saidclosure member, and work supporting means carried by said closuremember.

4. In a furnace structure, the combination of two co-operative chamberforming members movable into inter-engaging relation to form a closedchamber, a displaceable sealing medium carried by one of said membersand engaged by the other to seal said chamber and means for vibratingone of said members to facilitate displacement of said medium.

5. In a furnace structure, the combination of two co-operative chamberforming members movable into inter-engaging relation to form a closedchamber, a displaceable sealing medium carried by one of said membersand engaged by the other to seal said chamber, means for vibrating oneof said members during the inter-engaging movement of said members andmeans for interrupting said vibrating means upon full engagement of saidmembers.'

6. A furnace comprising a heat treating chamber having a channel at itsupper end for holding a displaceable sealing medium, a closure memberfor said chamber having a flange disposed in said sealing medium andremovable for access to said chamber and means carried by said closure'memb'er adapted to vibrate the same to facilitate displacement of saidsealing medium about said ange.

7. A furnace comprising a heating chamber having side walls, a muiiiedisposed Within said chamber, a channel at the upper end of said sidewalls for holding a displaceable sealing medium, a channel at the upperend of said muille for holding a displaceable sealing medium, a closuremember for said chamber and muiiie having depending flanges adapted tobe disposed in said sealing mediums, and means carried by said closuremember for vibrating said anges to facilitate the displacement of saidsealing medium thereabout.

8. A furnace comprising a heating chamber having side walls, a muffledisposed within said chamber, a channel at the upper end of said sidewalls for holding a displaceable sealing medium, a channel at the upperend of said muifle for holding a displaceable sealing medium, a closuremember for said chamber and muifle having depending flanges adapted tobe disposed in said sealing mediums, the iiange associated with saidfirst channel having a greater displacement than the flange associatedwith said second channel, whereby impact shock of said closure memberwill be received primarily by said side walls.

9. A furnace comprising a heating chamber having side walls, a muiiiedisposed within said chamber, a channel at the upper end of said sidewalls for holding a displaceable sealing medium, a channel at the upperend of said muiile for holding a displaceable sealing medium, a closuremember for saidachamber..andimuille having depending ilanges adaptedto'be disposed in said sealing ime'diums, :the`rising'e"lfass'o'ci'atedwithfsaid first channel being adapted toiengage-lits associE ated sealingmediumprior-to engagement of the angeassociated with said second channel with its associated sealing medium;vvherebyimpac't shock ofsaid closuremember v'vlillbe received primarilyby'said'sidewalis."

A furnace compri-sing"arheatinggchainber having an" openingdn'its`"uppe1'j,:end, a"cl'os'ure member for: saidopening'supported'independently of said. "chamber, a"botton1^' plateicarrie'd' .byA said closure' member' adjacent' the^center thereof:V andhaving-its' outered'ges free; saidplate being' exposedto the'direcrheatorsaidbnamberandbeing free to'expa'ri'dlaterallyrelativetosa'id'closure member.

11; A furnace comprising' a heating chamber havingr anopen'ing in" its'upper. end, .acclslure member forsaid'opening'suppor'ted indep, "d",Atlyof saidchamber, a bottomlplat'ecarriedb said closurelmember adjacentthecenter there'o'i and having itsoute'r edges freesaid4 plate being,exdosed-to. the heat OfSai'dLChamber-and being-4free tofeXpandlat-erallyrelative togsaid closuremember,` a channel disposed" abouttha upperedgeof 'said chamber for holdingaa.,displaoeablesealing mediumland aflangedependingfmm said?l plate for reception in saids'ealingI medium.

l2. A furnace comprising,awheatingechamber having an opening in itsupper end, a closure member for said opening supported independently ofsaid chamber, a bottom plate carried by said closure member adjacent thecenter thereof and having its outer edges free, said plate being exposedto the heat of said chamber and being free to expand laterally relativeto said closure member, a channel disposed about the upper edge of saidchamber for holding a displaceable sealing medium, a ange depending fromsaid plate for reception in said sealing medium and means for vibratingsaid plate to facilitate entrance of said iiange into said sealingmedium.

i3. A furnace comprising a combustion chamber, burners extendingtherein, a muilie having an open top disposed in said combustionchamber, a closure member extending over the top of said muiiie and saidcombustion chamber, a support for said closure member disposed remotelyfrom said combustion chamber, and means carried by said closure memberfor forming a gas seal between said mule and said combustion chamber andbetween said combustion chamber and said support.

14. A furnace comprising a heating chamber having a removable cover,means for introducing a gaseous medium into said chamber, a conduit insaid cover for egress of said medium, removable means positioned oversaid cover, adjacent to said conduit, for igniting the gaseous mediumescaping therefrom, and means operated by the removal and replacement ofsaid cover for moving said removable means to a position at one side ofsaid cover and back to a position over said cover.

l5. A furnace comprising a heating chamber having a removable cover,means for introducing a gaseous medium into said chamber, a conduit insaid cover for egress of said medium, means positioned over said cover,adjacent to said conduit, for igniting the gaseous medium escapingtherefrom, said last means being movable to a position at one side ofsaid cover to permit removal of the cover, and means for retaining saidmeans in each position.

Crl

1.6;;Affurnaoezcomprising asubstantially-cylindribalyShell,Iasrefractoryglining:within said shell forming.: a: chamber,Vheating,- means for said chamberyasubstantially-gewindricalmunie withinsaid'f chamberysa-id mulilehaving` an open top, ai'closureimembergextending. ,overy said muilie and said refraetoryqlining,means'fcarried by -said shell forrsupporting Aesaid closing'member outAof contactfiwithfsaid refractory-'lining and/said mufile, a Work supportcarried by said closure .member forsuspending the Workato be heatedWithin said muniey andmeansefor,:preventing gas vtransf er betweensaidgchamberfandsaid muflie. y

17.` Alfur-nace comprising a/,heat treating chamberfhaving-gamopening.therein for loading andlgunloadingf.theffurnace aremovable closuremember :'for vsaid openingi an .inlet conduit for introducingv a gaseousatmosphere into said cl1a1nber,=n a.vent-.forsaid chamber, meansV forcirculating said atmosphere Within; the chamber andI means:operate'dbyasaid closure member for controlling;l the; operation ofsaid circulating means...

18; i Afurnace. comprising` a, heat treating chamberihavingaan'openingtherein for loading .and unloadihgthexfurnace; aaremovable closuremember for'V said-opening?, means forintroducing a gaseousatmosphereintosaid' heat treating chambefr, means foricirculating saidatmosphere within the heat treating chamber and meansy operated upon theopeningoisaid closure member to interrupt the operationfofsaidcirculating means and upon theclosing offfsaid* closure member forrestarting the operation of said circulating means.

19. A furnace comprising a heat treating chamber having anopeningtherein for loading and unloading the furnance, a removable closuremember for said opening, means for introducing a gaseous atmosphere intosaid heat treating chamber, means for circulating said atmosphere withinthe heat treating chamber, means operated upon opening of said closuremember to interrupt the operation of said circulating means and upon theclosing of said closure member for restarting the operation of saidcirculating means, and means for delaying the restarting of saidcirculating means for a predetermined time after the closing of saidclosure means.

20. A furnace comprising a furnace casing having an opening therein, aheat treating chamber in said casing, a closure member for sai-d chamberextending into said opening, means for circulating a gaseous medium insaid chamber and means engageable by said closure member when in saidopening for controlling said circulating means.

21. A furnace comprising a furnace casing having an opening therein, aheat treating chamber in said casing, a seat Within said casing, aclosure member for said chamber extending into said opening and restingon said seat, means for circulating a gaseous medium in said chamber andswitch means engageable by said closure member on movement to and fromsaid seat for controlling said circulating means.

22. A furnace comprising a heat treating chamber, heating means for saidchamber, gas circulating means Within said chamber, a drive shaft forsaid circulating means extending through Wall of said chamber, a tubesurrounding said shaft and extending into said chamber, a seal for theouter end of said tube and gas non' retard-- ing means in said tubebetween said seal and said chamber.

23. A metallurgical furnace having a heat treating chamber, heatingmeans for said chamber, means for introducing a gaseous atmosphere intosaid chamber, and a revoluble fan Within said chamber for circulatingsaid gaseous atmosphere, said gas introducing means comprising a conduitdisposed about said fan and having inlets for directing the incomingatmosphere substantially in the direction of circulation of saidatmosphere as produced by said fan and substantially uniformly withrespect to the axis of said fan. l v

24. A furnace comprising an open top heat treating chamber, a removableclosure member forsaid chamber, means for introducing a gas atmosphereinto'said chamber, circulating means for said gas, a bale plate adjacentto and spaced from the top of said chamber and extending to adjacent thesides thereof for deiiecting the gases towards the side of said chamberand means for supporting said baille plate from said cover.

25. A furnace comprising an open top heat treating chamber, a removableclosure member for said chamber, means for introducing a gas atmosphereinto said chamber, circulating means for said gas, a bailleplateadjacent to and spaced from the top of said chamber and extendingto adjacent the sides thereof for deilecting the gases towards the sidesof said chamber, means for detachably supporting said bafe plate fromsaid cover, and work holding means carried below said baille plate. f

CHARLES E. THOMAS, JOHN S. FELIER. HAROLD J. NESS.

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